JP6409799B2 - Developer, image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to a developer (particularly a two-component developer), an image forming apparatus, and an image forming method.

  The image forming apparatus includes an image carrier. Toner contained in the developer is supplied to the electrostatic latent image formed on the surface of the image carrier. As a result, the electrostatic latent image is developed as a toner image. Subsequently, the toner image is transferred from the image carrier to the transfer target. The toner remaining on the image carrier after the transfer may cause dielectric breakdown of the photosensitive layer of the image carrier. When dielectric breakdown of the photosensitive layer is caused, black spots (so-called leak black spots) are generated in the formed image. Therefore, various studies have been made to suppress the occurrence of dielectric breakdown of the photosensitive layer.

  For example, the magnetic toner described in Patent Document 1 contains at least a binder resin, a wax component (release agent), and a magnetic material. There are 70 or more and 500 or less magnetic materials per 10,000 toner particles in the magnetic toner.

JP 2003-149857 A

  However, with the magnetic toner described in Patent Document 1, it is difficult to control the amount of the magnetic material released in the magnetic toner, and it is insufficient to suppress the occurrence of dielectric breakdown of the photosensitive layer. Moreover, since the magnetic toner described in Patent Document 1 contains a magnetic substance, it is difficult to apply the toner to colors other than black.

  The present invention has been made in view of the above-mentioned problems, suppresses the occurrence of black spots (particularly leaked black spots), improves image density and anti-fogging properties, and adheres external additive particles to the image carrier. It is an object to provide a developer that can be suppressed. Another object of the present invention is to provide an image forming apparatus and an image forming method using such a developer.

The developer according to the present invention includes a toner and a carrier. The carrier includes a plurality of carrier particles. The carrier particles have a carrier core and a carrier coat layer that covers the carrier core. The carrier coat layer includes a fluorine-containing resin. The toner includes a plurality of toner particles. The toner particles include toner base particles and a plurality of resin particles provided on the surface of the toner base particles. The number average primary particle diameter of the resin particles is 70 nm or more and 200 nm or less. The conductivity of a dispersion obtained by dispersing 0.1 g of the resin particles in 100 mL of distilled water is 2.5 μS / m or more and 6.0 μS / m or less. The aggregation degree Y ₁₆₀ of the resin particles represented by the following formula (1) is 15% by mass or more and 40% by mass or less.
Y ₁₆₀ = 100 × M _160A / M _160B (1)
(In the formula (1), M _160B represents the mass of the resin particles to which a pressure of 0.1 kgf / mm ² was applied for 5 minutes at a temperature of 160 ° C. M _160A represents 0.1 kgf for 5 minutes at a temperature of 160 ° C. The resin particles to which a pressure of / mm ² is applied are separated using a sieve having an opening of 75 μm, and represents the mass of the resin particles remaining on the sieve after the separation.)

  An image forming apparatus according to the present invention supplies an image carrier carrying a toner image and the toner contained in the developer to an electrostatic latent image formed on the surface of the image carrier, and A developing unit that develops the electrostatic latent image as the toner image. The image carrier is an amorphous silicon photoreceptor.

  In the image forming method according to the present invention, the developing unit supplies the toner contained in the developer to the electrostatic latent image formed on the surface of the image carrier, and converts the electrostatic latent image into a toner image. A developing step of developing as. The image carrier is an amorphous silicon photoreceptor.

  According to the developer, the image forming apparatus and the image forming method of the present invention, the occurrence of black spots (particularly leaked black spots) is suppressed, the image density and the fog resistance are improved, and the external additive particles adhere to the image carrier. Can be suppressed.

It is sectional drawing which shows the developing agent which concerns on embodiment of this invention. 1 is a diagram illustrating an example of a configuration of an image forming apparatus using a developer according to an embodiment of the present invention. (A) And (b) is a fragmentary sectional view which respectively shows the image carrier with which the image forming apparatus shown in FIG. 2 is provided. FIG. 3 is a diagram illustrating a developing unit and an image carrier provided in the image forming apparatus illustrated in FIG. 2.

  Embodiments of the present invention will be described below. However, the present invention is not limited to the following embodiments. The present invention can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, about the location where description overlaps, although description may be abbreviate | omitted suitably, the summary of invention is not limited. In the drawings, each component is schematically shown for easy understanding. The thickness, length, number, shape, dimension, and the like of each illustrated component are examples, and are not particularly limited.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. In addition, when “polymer” is added after the compound name to indicate the polymer name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof.

Hereinafter, the average value means a number average value unless otherwise specified. Also, the evaluation value (value indicating the shape or physical properties) of the powder (for example, toner, toner particles 2, toner base particles 3, resin particles 4, carrier particles 5 or carrier core 6 described later) is also defined. Otherwise, it means the number average value. The number average value is a value obtained by dividing the sum of the values measured for a considerable number of measurement objects by the number of measurements. Furthermore, the particle diameter of the powder is the equivalent-circle diameter of primary particles measured using an electron microscope unless otherwise specified. The equivalent circle diameter is the diameter of a circle having the same area as the projected area of the particles. The volume median diameter D ₅₀ is a median diameter calculated on a volume basis using a Coulter counter method. The volume median diameter D ₅₀ of the sample is measured using, for example, a precision particle size distribution measuring apparatus (“Coulter Counter Multisizer 3” manufactured by Beckman Coulter, Inc.).

<1. Developer>
The present embodiment relates to the developer 1. Hereinafter, the developer 1 of this embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the developer 1 of this embodiment. Developer 1 includes toner and carrier. The toner includes a plurality of toner particles 2. The toner is an aggregate (powder) of a large number of toner particles 2. The carrier includes a plurality of carrier particles 5. The carrier is an aggregate (powder) of a large number of carrier particles 5.

<1-1. Toner particles>
The toner particles 2 include toner base particles 3 and a plurality of resin particles 4. The plurality of resin particles 4 are provided on the surface of the toner base particles 3. In FIG. 1, the resin particles 4 are shown with dots, and a part of the reference numerals is omitted.

<1-1-1. Resin particles>
The resin particles 4 are provided on the surface of the toner base particles 3 as external additive particles. The resin particles 4 function as spacer particles, for example. Since the resin particles 4 have a predetermined number average primary particle diameter, conductivity, and aggregation degree Y ₁₆₀ , the occurrence of dielectric breakdown of the photosensitive layer 112 of the image carrier 11 is suppressed, and the occurrence of leak black spots in the formed image is suppressed. can do.

In order to facilitate understanding, first, the dielectric breakdown of the photosensitive layer 112 (see FIG. 3) will be described. Hereinafter, a case where an image is formed using the image forming apparatus 100 (see FIG. 2) including the image carrier 11 (see FIG. 2, for example, a photoreceptor) and a cleaning unit 16 (see FIG. 2, for example, a cleaning blade) will be described. An example will be described. After toner transfer, the toner remaining on the image carrier 11 is cleaned by the cleaning unit 16. The image carrier 11 is in contact with the tip portion (ridge line portion) of the cleaning unit 16. The toner remaining on the image carrier 11 tends to stay in a region where the image carrier 11 and the tip of the cleaning unit 16 are in contact with each other. The staying toner may be rubbed by the cleaning unit 16 and overcharged. The overcharged toner discharges toward the local region of the image carrier 11 (so-called single point discharge) when the toner charge amount threshold is exceeded. This causes dielectric breakdown in the photosensitive layer 112 of the image carrier 11. The dielectric breakdown of the photosensitive layer 112 is more likely to occur when the image carrier 11 is an amorphous silicon photoreceptor, compared to an organic photoreceptor. In order to suppress the occurrence of dielectric breakdown of the photosensitive layer 112, it is useful to control the number average primary particle size, conductivity and cohesion Y ₁₆₀ of the resin particles 4. Hereinafter, the number average primary particle diameter, conductivity, and aggregation degree Y ₁₆₀ of the resin particles 4 will be described.

(Number average primary particle size)
The number average primary particle diameter of the resin particles 4 is 70 nm or more and 200 nm or less. When the number average primary particle diameter of the resin particles 4 is less than 70 nm, the resin particles 4 hardly function as a spacer. For this reason, particularly when images with a low printing rate are continuously formed, the toner tends to stay in the developing unit 14 (see FIG. 2) of the image forming apparatus 100 for a long time and the toner tends to deteriorate. Therefore, the toner cannot be charged to a desired value, and the image density of the formed image is lowered. When the number average primary particle diameter of the resin particles 4 exceeds 200 nm, the resin particles 4 are easily detached from the toner base particles 3. Therefore, there is a tendency that dielectric breakdown of the image carrier 11 is caused. As a result, leak black spots occur in the formed image. Further, when the number average primary particle diameter of the resin particles 4 exceeds 200 nm, it is considered that the fluidity of the toner is lowered.

  The number average primary particle diameter of the resin particles 4 is adjusted, for example, by changing one or both of the reaction time and the stirring conditions when the raw materials of the resin particles 4 are reacted. For example, the longer the reaction time, the larger the number average primary particle size of the resin particles 4. The method for measuring the number average primary particle diameter of the resin particles 4 is the same method as in Examples described later or an alternative method thereof.

(conductivity)
The conductivity of a dispersion obtained by dispersing 0.1 g of resin particles 4 in 100 mL of distilled water is 2.5 μS / m or more and 6.0 μS / m or less. The conductivity of the dispersion in which the resin particles 4 are dispersed is preferably 3.0 μS / m or more and 5.0 μS / m or less. When the electrical conductivity of the dispersion of the resin particles 4 is less than 2.5 μS / m, the charge of the resin particles 4 is difficult to escape. For this reason, the toner particles 2 having the resin particles 4 are rubbed by the cleaning unit 16 on the image carrier 11, whereby the toner particles 2 are overcharged and the dielectric breakdown of the image carrier 11 may be caused. As a result, a leak black spot is generated in the formed image. When the electrical conductivity of the dispersion of the resin particles 4 exceeds 6.0 μS / m, components such as an emulsifier in the resin particles 4 may ooze out and adhere to the carrier particles 5. As a result, the carrier particles 5 cannot satisfactorily charge the toner particles 2 and fog may occur in the formed image. Since the conductivity is inversely proportional to the electrical resistance, the electrical conductivity of the dispersion of the resin particles 4 is an index representing the electrical resistance of the resin particles 4. The difference in conductivity of the dispersion of resin particles 4 tends to appear larger than the difference in electrical resistance of resin particles 4. Therefore, it is considered that the electrical resistance of the resin particles 4 can be controlled with high accuracy by controlling the conductivity of the dispersion of the resin particles 4. When the electrical conductivity of the dispersion of the resin particles 4 is 2.5 μS / m or more and 6.0 μS / m or less, the electric resistance of the resin particles 4 is relatively low.

  The conductivity of the dispersion of the resin particles 4 is adjusted by changing the amount of emulsifier (dispersant) added when the resin particles 4 are produced, for example. As the amount of the emulsifier added relative to the amount of the monomer (for example, acrylic acid or acrylic acid derivative) for forming the resin particles 4 increases, the conductivity of the dispersion of the resin particles 4 tends to increase. Further, the conductivity of the dispersion of the resin particles 4 is also adjusted, for example, by changing the washing conditions when washing the resin particles 4 and changing the amount of the emulsifier remaining on the surface of the resin particles 4. . The method for measuring the conductivity of the dispersion of the resin particles 4 is the same method as in the examples described later or an alternative method thereof.

(Cohesion degree)
The aggregation degree Y ₁₆₀ of the resin particles 4 is 15% by mass or more and 40% by mass or less. The aggregation degree Y ₁₆₀ of the resin particles 4 is preferably 15% by mass or more and 30% by mass or less. The aggregation degree Y ₁₆₀ of the resin particles is represented by the following formula (1). In the formula (1), M _160B represents the mass of the resin particles 4 to which a pressure of 0.1 kgf / mm ² is applied for 5 minutes at a temperature of 160 ° C. M _160A is a sieve having a mesh size of 75 μm (200 mesh defined by JIS Z8801-1, a wire diameter of 50 μm and a plain weave square sieve) applied with a pressure of 0.1 kgf / mm ² for 5 minutes at a temperature of 160 ° C. It represents the mass of the resin particles 4 separated on the sieve after separation and remaining on the sieve after separation.
Y ₁₆₀ = 100 × M _160A / M _160B (1)

When the aggregation degree Y ₁₆₀ of the resin particles 4 is less than 15% by mass, the resin particles 4 have high hardness, and the toner particles 2 having the resin particles 4 are easily rubbed by the cleaning unit 16 on the image carrier 11. For this reason, the resin particles 4 are overcharged and the dielectric breakdown of the image carrier 11 tends to be caused. As a result, a leak black spot is generated in the formed image.

When the degree of aggregation Y ₁₆₀ of the resin particles 4 exceeds 40% by mass, the hardness of the resin particles 4 decreases, and the resin particles 4 detached from the toner base particles 3 onto the image carrier 11 are cleaned with the image carrier 11. It becomes easy to be thermally compressed at the contact portion with the portion 16. Therefore, the resin particles 4 are likely to stick to the image carrier 11. As a result, white spots occur in the formed image. When the resin particles 4 are thermally compressed at the contact portion between the image carrier 11 and the cleaning unit 16, the energy applied to the resin particles 4 is a pressure of 0.1 kgf / mm ² for 5 minutes at a temperature of 160 ° C. It is estimated that this corresponds to the energy when. Therefore, in order to suppress the aggregation of the resin particles 4 caused when the resin particles 4 are thermally compressed, it is considered important to control the aggregation degree Y ₁₆₀ of the resin particles 4 at 160 ° C. For example, when a plurality of types of resin particles are compared, the aggregation degree Y _{160 at} 160 ° C. differs even if the aggregation degree in the temperature region below 160 ° C. is the same.

Further, when the aggregation degree Y ₁₆₀ of the resin particles 4 exceeds 40% by mass, the resin particles 4 are likely to adhere to the carrier particles 5. In the carrier particles 5 of the developer 1 of this embodiment, the carrier coat layer 7 contains a fluorine-containing resin. The hardness of such a carrier coat layer 7 tends to be low. Therefore, the contact between the toner particles 2 having the resin particles 4 and the carrier particles 5 tends to cause the carrier coat layer 7 to be scraped and the resin particles 4 to adhere to the carrier coat layer 7.

The aggregation degree Y ₁₆₀ of the resin particles 4 is adjusted, for example, by changing the amount of the crosslinking agent added when the resin particles 4 are produced. Since the crosslinking reaction proceeds more easily as the addition amount of the crosslinking agent increases, the hardness of the resin particles 4 tends to increase, and the aggregation degree Y ₁₆₀ of the resin particles 4 tends to decrease. Also, the higher the purity of the cross-linking agent, the more easily the cross-linking reaction proceeds. Therefore, the hardness of the resin particles 4 tends to increase, and the aggregation degree Y ₁₆₀ of the resin particles 4 tends to decrease.

Method of measuring the cohesion Y ₁₆₀ of the resin particles 4 are the same method or an alternative method to Example described below. Even after the resin particles 4 are externally added, the resin particles 4 can be separated from the toner particles 2 and the aggregation degree Y ₁₆₀ of the resin particles 4 can be measured. An example of a method for separating the resin particles 4 from the toner particles 2 will be described. Specifically, the toner is added to an aqueous solution containing a surfactant to obtain a mixture. The mixture is dispersed using an ultrasonic disperser. The resulting dispersion is filtered and the filtrate is recovered. The collected filtrate is centrifuged using a centrifuge. The supernatant liquid containing the resin particles 4 is collected. The supernatant liquid is filtered under pressure to obtain a wet cake of resin particles 4. The obtained resin particles 4 are dried in a vacuum to obtain dried resin particles 4.

Examples of the resin constituting the resin particle 4 include styrene acrylic resin, styrene resin, vinyl resin, polyester resin, urethane resin, acrylonitrile resin, and acrylamide resin. Among them, cohesion Y ₁₆₀ of the resin particles 4, the conductivity and the number average primary particle diameter because it easily adjusted to the desired range, styrene resin or styrene-acrylic acid resin, more styrene acrylic resin preferable. The resin particles 4 are obtained by polymerizing or copolymerizing monomers for forming the resin particles 4.

  The styrenic resin is obtained, for example, by polymerizing or copolymerizing one or more styrenic monomers. The monomer for forming the resin particles 4 is a styrene monomer. The styrenic monomer is styrene or a styrene derivative. Examples of styrenic monomers include styrene, α-methylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene or p-tert- Butyl styrene is mentioned.

  The styrene acrylic acid resin is obtained, for example, by copolymerizing one or more styrene monomers and one or more acrylic monomers. Monomers for forming the resin particles 4 are a styrene monomer and an acrylic acid monomer. The styrenic monomer is styrene or a styrene derivative. The styrene monomer is the same as the example of the styrene monomer for forming the styrene resin. Of the styrenic monomers, styrene is preferred. The acrylic acid monomer is acrylic acid or an acrylic acid attractant. Examples of acrylic monomers include methacrylic acid, methacrylic acid alkyl esters, acrylic acid or acrylic acid alkyl esters. Examples of alkyl methacrylates include methyl methacrylate, ethyl methacrylate, butyl methacrylate, isopropyl methacrylate or 2-ethylhexyl methacrylate. Examples of alkyl acrylate esters include methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, octyl acrylate, or 2-ethylhexyl acrylate. Among the acrylic monomers, methacrylic acid alkyl esters are preferable, and butyl methacrylate is more preferable. The content of the styrene monomer is preferably 5 parts by mass or more and 50 parts by mass or less, with respect to 100 parts by mass of the acrylic acid monomer (acrylic acid or acrylic acid derivative). It is more preferable that the amount is not more than part by mass.

A cross-linking agent may be used to form the styrene acrylic acid resin. By using a cross-linking agent, the degree of cross-linking of the resin can be increased, and the degree of aggregation Y ₁₆₀ of the resin particles 4 can be reduced. Examples of the crosslinking agent include compounds having two or more vinyl groups (preferably two or three, more preferably two). Specific examples of the compound having two or more vinyl groups include divinylbenzene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate or trimethylolpropane trimethacrylate. It is done. Of these, divinylbenzene is preferred as the crosslinking agent.

Since it is easy to adjust the aggregation degree Y ₁₆₀ of the resin particles 4 to a desired value, the content of the crosslinking agent is 35 parts by mass with respect to 100 parts by mass of the acrylic acid monomer (acrylic acid or acrylic acid derivative). The amount is preferably 85 parts by mass or less.

The purity of the crosslinking agent used for forming the styrene acrylic acid resin is preferably 80% or more, and more preferably 98% or more. When the purity of the crosslinking agent is within such a range, the degree of aggregation Y ₁₆₀ of the styrene acrylic acid resin particles formed can be reduced. The purity of the crosslinking agent is, for example, the ratio between the peak characteristic of the crosslinking agent and the peak derived from impurities using ¹ H-NMR (proton nuclear magnetic resonance spectrometer, “600CSL type” manufactured by Agilent Technologies). Is calculated from

Since the aggregation degree Y ₁₆₀ , conductivity, and number average primary particle diameter of the resin particles 4 can be easily adjusted to the desired ranges, the resin particles 4 are composed of an acrylic acid monomer, a styrene monomer, and a crosslinking agent. And a copolymer thereof. For the same reason, the resin particle 4 has an acrylic acid alkyl ester or methacrylic acid alkyl ester (more preferably butyl methacrylate), styrene, and two or more vinyl groups (preferably two or three, more preferably More preferably, it is a copolymer with a compound having 2).

  One type of resin particles 4 may be used alone, or two or more types of resin particles 4 may be used in combination. The content (addition amount) of the resin particles 4 is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, and 0.5 parts by mass or more with respect to 100.0 parts by mass of the toner base particles 3. More preferably, it is 2.0 parts by mass or less.

(Other external additives)
The surface of the toner base particles 3 may be further provided with an external additive (other external additives) other than the resin particles 4 as necessary. Examples of other external additives include silica or metal oxide. Specific examples of the metal oxide include alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate. The surface of other external additives may be hydrophobized. One type of other external additives may be used alone, or two or more types of other external additives may be used in combination.

  The number average particle size of the other external additives is preferably 1 nm or more and 1 μm or less, and more preferably 1 nm or more and 50 nm or less. The amount of other external additives used is preferably 0.5 parts by mass or more and 10.0 parts by mass or less with respect to 100.0 parts by mass of the toner base particles.

<1-1-2. Toner mother particles>
The toner base particles 3 may contain, for example, one or more of a binder resin, a colorant, a release agent, and a charge control agent. However, unnecessary components may be omitted depending on the use of the toner. The toner base particles 3 may be encapsulated. The encapsulated toner base particle 3 has, for example, a toner core having the same structure and components as those of the toner base particle described below, and a shell layer (capsule layer) formed on the surface of the toner core.

(Binder resin)
The binder resin is not particularly limited as long as it is a binder resin used for toner preparation. As the binder resin, a thermoplastic resin is preferable from the viewpoint of improving the fixing property of the toner. Examples of the thermoplastic resin include acrylic acid resins, styrene acrylic acid resins, polyester resins, polyamide resins, urethane resins, and vinyl alcohol resins. A polyester resin is particularly preferable as the binder resin in terms of improving the dispersibility of the colorant, the chargeability of the toner, and the fixability of the toner to the recording medium (for example, paper). Hereinafter, the polyester resin will be described.

  The polyester resin can be obtained by, for example, condensation polymerization or co-condensation polymerization of alcohol and carboxylic acid.

  Examples of the alcohol used when synthesizing the polyester resin include a dihydric alcohol or a trihydric or higher alcohol.

  Examples of the dihydric alcohol include diols or bisphenols. Examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1, Examples include 5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol. Examples of bisphenols include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct (polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane) or bisphenol A propylene oxide addition Things.

  Examples of trihydric or higher alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane or 1,3,5-trihydroxymethyl Benzene is mentioned.

  Examples of the carboxylic acid used when synthesizing the polyester resin include a divalent carboxylic acid or a trivalent or higher carboxylic acid.

  Examples of divalent carboxylic acids include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid. Examples include acids, alkyl succinic acids or alkenyl succinic acids. Examples of alkyl succinic acids include n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid or isododecyl succinic acid. Examples of alkenyl succinic acids include n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid or isododecenyl succinic acid.

  Examples of trivalent or higher carboxylic acids include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalene tricarboxylic acid, 1,2,4-naphthalene tricarboxylic acid, 4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, Examples include 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid or emporic trimer acid.

  Alcohol and carboxylic acid may be used individually by 1 type, respectively, and may be used in combination of 2 or more type. Furthermore, the carboxylic acid may be derivatized into an ester-forming derivative. Examples of ester-forming derivatives include acid halides, acid anhydrides (eg, trimellitic anhydride) or lower alkyl esters. Here, “lower alkyl” means an alkyl group having 1 to 6 carbon atoms.

  When a polyester resin is used as the binder resin, the content of the polyester resin in the binder resin is preferably 70% by mass or more, more preferably 80% by mass or more, and 90% by mass or more. Particularly preferred is 100% by mass.

  The softening point (Tm) of the binder resin is preferably 60 ° C. or higher and 150 ° C. or lower. A plurality of types of resins having different softening points can be used in combination so that the softening point of the binder resin is within such a range.

  The acid value of the binder resin is preferably 1 mgKOH / g or more and 30 mgKOH / g or less. The acid value of the binder resin is measured, for example, by the method described in JIS (Japanese Industrial Standard) K0070-1992.

  The melting point (Mp) of the binder resin is preferably 50 ° C. or higher and 100 ° C. or lower. When the melting point of the binder resin is within such a range, the toner can easily have low-temperature fixability, hot offset resistance and heat-resistant storage stability. The melting point of the binder resin is measured using, for example, a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.). Specifically, put a measurement sample (binder resin) in an aluminum dish. Set the aluminum pan on the measurement part of the differential scanning calorimeter. Use an empty aluminum pan for reference. The temperature is increased to 170 ° C. at a rate of 10 ° C./min with 30 ° C. as the measurement start temperature. The maximum peak temperature of the heat of fusion observed when the temperature is raised is taken as the melting point of the measurement sample.

(Coloring agent)
As the colorant, a known pigment or dye is used according to the color of the toner. The content of the colorant is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

  When the toner is a black toner, a black colorant is used. An example of a black colorant is carbon black. You may use the black colorant adjusted to black using the yellow colorant, magenta colorant, and cyan colorant which are mentioned later.

  When the toner is yellow toner, a yellow colorant is used. Examples of yellow colorants include condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, or arylamide compounds. More specifically, C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191 or 194), naphthol yellow S, Hansa yellow G or C.I. I. Bat yellow is mentioned.

  If the toner is magenta toner, a magenta colorant is used. Examples of magenta colorants include condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds or perylene compounds. More specifically, C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254).

  When the toner is cyan toner, a cyan colorant is used. Examples of cyan colorants include copper phthalocyanine, copper phthalocyanine derivatives, anthraquinone compounds or basic dye lake compounds. More specifically, C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62 or 66), phthalocyanine blue, C.I. I. Bat Blue or C.I. I. Acid blue.

(Release agent)
The release agent is used, for example, for the purpose of improving the toner fixing property and offset resistance. In order to improve the toner fixing property and offset resistance, the content of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

  Examples of mold release agents include aliphatic hydrocarbon waxes, oxides of aliphatic hydrocarbon waxes, vegetable waxes, animal waxes, mineral waxes, waxes based on fatty acid esters or part or all of fatty acid esters. An oxidized wax may be mentioned. Examples of aliphatic hydrocarbon waxes include ester wax, polyethylene wax (eg low molecular weight polyethylene), polypropylene wax (eg low molecular weight polypropylene), polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax or Fischer-Tropsch A wax is mentioned. Examples of the oxide of the aliphatic hydrocarbon wax include an oxidized polyethylene wax or a block copolymer of oxidized polyethylene. Examples of plant waxes include candelilla wax, carnauba wax, wood wax, jojoba wax or rice wax. Examples of animal waxes include beeswax, lanolin or whale wax. Examples of mineral waxes include ozokerite, ceresin or petrolatum. Examples of the wax mainly composed of a fatty acid ester include montanic acid ester wax and caster wax. Deoxidized carnauba wax is an example of a wax in which a part or all of the fatty acid ester has been deoxidized. A mold release agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  The melting point (melting temperature) of the release agent is preferably 50 ° C. or higher and 100 ° C. or lower. When the melting point of the release agent is within such a range, the low-temperature fixability of the toner containing the release agent is improved, and the occurrence of offset at a high temperature of the toner tends to be suppressed. The melting point of the release agent can be measured using, for example, a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.).

(Charge control agent)
The charge control agent is used for the purpose of improving the charge level and the charge rising property. Further, it is used for the purpose of obtaining a toner excellent in durability and stability. The charge rising characteristic is an index as to whether or not charging to a predetermined charge level is possible in a short time.

  When developing with positively charged toner, it is preferable to use a positively chargeable charge control agent. On the other hand, when developing using a negatively charged toner, it is preferable to use a negatively chargeable charge control agent. However, when sufficient chargeability is ensured in the toner, the charge control agent may not be used.

  Examples of positively chargeable charge control agents include azine compounds, direct dyes made of azine compounds, nigrosine compounds, acid dyes made of nigrosine compounds, metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, alkylamides or quaternary An ammonium salt is mentioned. Further, a resin having a quaternary ammonium salt, a carboxylate or a carboxyl group can also be used as a positively chargeable charge control agent. In order to obtain quick start-up property, the charge control agent is preferably a quaternary ammonium salt or a nigrosine compound. One type of charge control agent may be used alone, or a plurality of types of charge control agents may be used in combination. The content of the charge control agent is preferably 0.05 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the binder resin.

<1-2. Carrier particles>
The carrier particle 5 has a carrier core 6 and a carrier coat layer 7. The carrier core 6 is covered with a carrier coat layer 7. The carrier coat layer 7 is provided on the surface of the carrier core 6.

  The number average primary particle diameter of the carrier particles 5 is preferably 20 μm or more and 120 μm or less, and more preferably 25 μm or more and 80 μm or less. The number average primary particle diameter of the carrier particles 5 is measured by, for example, the same method as the measurement of the number average primary particle diameter of the resin particles 4.

  When the toner is used in the two-component developer, the toner content is preferably 3% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less with respect to the mass of the two-component developer. It is more preferable.

<1-2-1. Carrier coat layer>
The carrier coat layer 7 contains a fluorine-containing resin. Examples of the fluorine-containing resin include a copolymer of tetrafluoroethylene and hexafluoropropylene or a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether. Examples of the perfluoroalkyl vinyl ether as a monomer are vinyl ethers having a perfluoroalkyl having 1 to 20 carbon atoms, and more specifically perfluorooctyl vinyl ether.

  When the fluorine-containing resin is perfluoroalkyl vinyl ether, the content of perfluoroalkylate (for example, perfluorooctanoic acid) is preferably 100 ppm or less with respect to the mass of the perfluoroalkyl vinyl ether, and is 10 ppm or less. It is more preferable. The content of perfluoroalkylate is measured by, for example, a high performance liquid chromatograph mass spectrometer (LC / MS).

  The carrier coat layer 7 may further contain a resin other than the fluorine-containing resin (hereinafter sometimes referred to as other resin). Examples of other resins include acrylic acid polymers, styrene polymers, styrene-acrylic acid copolymers, olefin polymers, polyvinyl chloride, polyvinyl acetate, polycarbonate, cellulose resins, polyester resins, and unsaturated resins. Examples include polyester resin, polyamide resin, polyamideimide resin, polyimide resin, urethane resin, epoxy resin, silicone resin, fluorine resin, phenol resin, xylene resin, diallyl phthalate resin, polyacetal resin, or amino resin. Examples of olefin polymers include polyethylene, chlorinated polyethylene, or polypropylene. Examples of the fluororesin include polytetrafluoroethylene, polychlorotrifluoroethylene, or polyvinylidene fluoride. These resins can be used alone or in combination of two or more. As other resin, a polyamideimide resin is preferable, and a copolymer of trimellitic anhydride and 4,4′-diaminodiphenylmethane is more preferable.

  When the carrier coat layer 7 contains a fluorine-containing resin and another resin, the content of the fluorine-containing resin is preferably 1 part by mass or more and 9 parts by mass or less with respect to 1 part by mass of the other resin. When the content of the fluorine-containing resin is 1 part by mass or more with respect to 1 part by mass of the other resin, the toner particles 2 are easily easily charged by friction with the carrier particles 5. When the content of the fluorine-containing resin is 9 parts by mass or less with respect to 1 part by mass of the other resin, the fluorine-containing resin is easily dispersed in the other resin.

  The fluorine-containing resin may be contained in the carrier coat layer 7 while maintaining the shape of the particles. For example, the carrier coat layer 7 in which particles of fluorine-containing resin are dispersed in other resin may be used.

<1-2-2. Career Core>
Examples of the carrier core 6 include particles of iron, iron oxide (eg, ferrite), reduced iron, magnetite, copper, silicon steel, nickel or cobalt; these materials and metals (eg, manganese, magnesium, strontium, zinc or aluminum) ) Particles of iron-nickel alloy; particles of iron-cobalt alloy; particles of ceramics; or particles of a high dielectric constant material. Examples of ceramics include titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, magnesium titanate, barium titanate, lithium titanate, lead titanate, lead zirconate or lithium niobate Is mentioned. Examples of the high dielectric constant material include ammonium dihydrogen phosphate, potassium dihydrogen phosphate, or Rochelle salt. Among these, ferrite or an alloy containing ferrite is preferable. These carrier cores 6 may be used alone or in combination of two or more.

<2. Developer production method>
Hereinafter, an example of a method for producing the developer 1 will be described. In the production of the developer 1, toner particles 2 and carrier particles 5 are produced. Then, the toner particles 2 and the carrier particles 5 are mixed to obtain the developer 1.

<2-1. Production of toner particles>
In the production of the toner particles 2, the toner base particles 3 and the resin particles 4 are produced. Then, the resin particles 4 are attached to the surface of the toner base particles 3 to obtain the toner particles 2.

(Manufacture of toner mother particles)
Preferable examples of the method for producing the toner base particles 3 include a pulverization method or an aggregation method. In these methods, it is easy to favorably disperse the colorant, the charge control agent, and the release agent in the binder resin.

  In an example of the pulverization method, first, a binder resin, a colorant, a charge control agent, and a release agent are mixed. Subsequently, the obtained mixture is melt-kneaded using a melt-kneading apparatus (for example, a single-screw or twin-screw extruder). Subsequently, the obtained melt-kneaded product is pulverized and classified. Thereby, toner base particles 3 are obtained. When the pulverization method is used, the toner base particles 3 can often be manufactured more easily than when the aggregation method is used.

  In an example of the aggregation method, first, these fine particles are aggregated in an aqueous medium containing fine particles of a binder resin, a colorant, a charge control agent, and a release agent until a desired particle diameter is obtained. Thereby, aggregated particles containing a binder resin, a colorant, a charge control agent, and a release agent are formed. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. Thereby, toner mother particles 3 having a desired particle diameter are obtained. If necessary, the obtained toner base particles 3 are washed, and the washed toner base particles 3 are dried. In the case where a spray dryer is used in the drying step, drying and external addition can be performed simultaneously by spraying a dispersion of an external additive (for example, a large number of resin particles 4) onto the toner base particles 3.

  The encapsulated toner base particles 3 may be manufactured by forming a shell layer on the surface of the toner core corresponding to the toner base particles 3. The method for forming the shell layer is arbitrary. For example, the shell layer may be formed using any of an in-situ polymerization method, a submerged cured coating method, and a coacervation method.

(Manufacture of resin particles)
The resin particles 4 are produced, for example, by polymerizing or copolymerizing the monomers for forming the resin particles 4 already described. Hereinafter, the case where the resin particles 4 are styrene acrylic acid resin particles will be described as an example.

  In the production of styrene acrylic acid resin particles, an acrylic acid monomer and a styrene monomer are reacted (copolymerized). Thereby, a large number of resin particles 4 of styrene acrylic acid resin are formed. In the copolymerization reaction, for example, an acrylic acid monomer and a styrene monomer are stirred while heating in a solvent. In the copolymerization reaction, a crosslinking agent, an emulsifier, and a polymerization initiator may be added as needed in addition to the acrylic acid monomer and the styrene monomer. In order to suitably proceed the copolymerization reaction, the copolymerization reaction is preferably performed in a nitrogen atmosphere. One acrylic acid monomer may be used alone, or two or more acrylic acid monomers may be used in combination. Moreover, a styrene-type monomer may also be used individually by 1 type, and may be used in combination of 2 or more type.

  The addition amount of the styrene monomer (styrene or styrene derivative) is preferably 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the acrylic acid monomer (acrylic acid or acrylic acid derivative). More preferably, it is 10 to 30 parts by mass.

It is preferable to add a crosslinking agent in addition to the acrylic acid monomer and the styrene monomer. By using a crosslinking agent, it becomes easy to adjust the crosslinking degree of the styrene acrylic resin formed. This makes it easier to adjust the degree of aggregation Y ₁₆₀ of the resin particles 4 to a desired value. As the crosslinking agent, a monomer having two or more vinyl groups (preferably two or three, more preferably two) is preferable, and divinylbenzene is more preferable. A crosslinking agent may be used individually by 1 type, and may be used in combination of 2 or more type. Since the aggregation degree Y ₁₆₀ of the resin particles 4 can be easily adjusted to a desired value, the addition amount of the crosslinking agent is 35 parts by mass with respect to 100 parts by mass of the acrylic acid monomer (acrylic acid or acrylic acid derivative). The amount is preferably 85 parts by mass or less.

  When an emulsifier is used in the copolymerization reaction, examples of the emulsifier include sulfonate-containing emulsifiers. More specifically, sodium dodecylbenzenesulfonate, sodium laurylsulfonate, di (2-ethylhexyl) sulfosuccinate Sodium or sodium isooctylbenzene sulfonate can be mentioned. As the emulsifier, sodium dodecylbenzenesulfonate is preferable because the conductivity of the dispersion of the resin particles 4 can be easily adjusted to a desired value. Since it is easy to adjust the conductivity of the dispersion of the resin particles 4 to a desired value, the amount of the emulsifier added is 4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the acrylic acid monomer. Is preferred.

  When a polymerization initiator is used for the copolymerization reaction, examples of the polymerization initiator include benzoyl peroxide, t-butyl hydroperoxide, potassium persulfate, ammonium persulfate, or hydrogen peroxide. As the polymerization initiator, benzoyl peroxide is preferable. The addition amount of the polymerization initiator is preferably 10 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the acrylic monomer.

  An example of the solvent used in the copolymerization reaction includes an aqueous medium. The aqueous medium is a medium mainly composed of water. The aqueous medium may function as a solvent or may function as a dispersion medium. Specific examples of the aqueous medium include water or a mixed liquid of water and a polar solvent. Examples of the polar solvent contained in the aqueous medium include methanol or ethanol. The content of water in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass with respect to the mass of the aqueous medium. In order to suitably proceed the copolymerization reaction, it is preferable to use water as a solvent. In order to suitably proceed the copolymerization reaction, the amount of the solvent added is preferably 200 parts by mass or more and 1000 parts by mass or less, and 500 parts by mass or more and 700 parts by mass with respect to 100 parts by mass of the acrylic acid monomer. It is more preferable that the amount is not more than part by mass.

  The number average primary particle diameter of the resin particles 4 to be formed can be adjusted by changing one or both of the reaction time of the copolymerization reaction and the stirring conditions. When the reaction time in the copolymerization reaction is lengthened, the number average primary particle diameter of the formed resin particles 4 tends to increase. When the stirring speed in the copolymerization reaction is decreased, the number average primary particle diameter of the formed resin particles 4 tends to increase.

  In order to allow the copolymerization reaction to proceed appropriately, the reaction temperature of the copolymerization reaction is preferably 70 ° C. or higher and 100 ° C. or lower, and more preferably 85 ° C. or higher and 95 ° C. or lower. For the same reason, the reaction time of the copolymerization reaction is preferably 1 hour or more and 5 hours or less.

(External)
The toner base particles 3 and the resin particles 4 are mixed using a mixer (for example, an FM mixer manufactured by Nippon Coke Industries, Ltd.). The mixing condition is preferably set to a condition in which the resin particles 4 are not completely buried in the toner base particles 3. A plurality of resin particles 4 are adhered to the surface of the toner base particles 3 by mixing. As a result, toner particles 2 are obtained.

<2-2. Production of carrier particles>
In the manufacture of the carrier particles 5, the carrier core 6 is covered with the carrier coat layer 7. First, the carrier core 6 is prepared. Subsequently, a liquid for forming the carrier coat layer 7 (hereinafter sometimes referred to as a carrier coat layer forming liquid) is prepared. Specifically, a fluorine-containing resin is dispersed in an aqueous medium. Other resins may be added to the carrier coat layer forming liquid. In order to disperse the fluorine-containing resin satisfactorily, a surfactant (preferably a nonionic surfactant) may be added to the carrier coat layer forming liquid. Subsequently, using a fluidized bed coating apparatus, a carrier coat layer forming liquid is sprayed onto the carrier core. As a result, the carrier core is covered with an uncured organic layer (fluidized bed). The carrier core covered with the uncured organic layer (fluidized bed) is heated using a dryer. Thereby, the fluidized bed is cured. As a result, carrier particles 5 having a carrier core 6 and a carrier coat layer 7 covering the carrier core 6 are obtained.

<2-3. Mixing toner and carrier>
The toner (many toner particles 2) and the carrier (many carrier particles 5) are mixed using a mixer (for example, a rocking mixer (registered trademark) or a ball mill). As a result, developer 1 is obtained.

  In the manufacturing method of the developer 1, unnecessary steps may be omitted. For example, when a commercially available product can be used as a material as it is, the step of preparing the material can be omitted by using a commercially available product. In order to efficiently produce the developer 1, it is preferable to form a large number of particles (toner particles 2 or carrier particles 5) simultaneously.

<3. Image Forming Apparatus and Image Forming Method>
Hereinafter, an image forming apparatus 100 and an image forming method using the developer 1 according to the present embodiment will be described with reference to FIG. FIG. 2 shows an example of the configuration of the image forming apparatus 100. The image forming apparatus 100 includes, for example, an image carrier 11 and a developing unit 14. In the image forming apparatus 100, the developer 1 of this embodiment is used. The developer 1 is stored in the developing unit 14. The image forming apparatus 100 includes a charging unit 12, an exposure unit 13, a transfer unit (only the primary transfer unit 15, or both the primary transfer unit 15 and the secondary transfer unit 18), a cleaning unit 16, and a transfer belt 17. The fixing unit 19 may be further provided.

  In the image forming method using the image forming apparatus 100, a developing process is performed. In the image forming method, one or more of a charging process, an exposure process (electrostatic latent image forming process), a transfer process, and a fixing process may be further performed.

  In the charging step, the charging unit 12 charges the surface of the image carrier 11. Examples of the charging unit 12 include a non-contact type charging unit (for example, a corotron charger or a scorotron charger) or a contact type charging unit (for example, a charging roller or a charging brush). The charging polarity of the charging unit 12 is not particularly limited. For example, the charging unit 12 charges the surface of the image carrier 11 to positive polarity, and the toner charged to the positive polarity is supplied to the surface of the image carrier 11 by the developing unit 14 so that the electrostatic latent image is used as a toner image. You may develop.

  In the exposure step (electrostatic latent image forming step), the exposure unit 13 exposes the charged surface of the image carrier 11. As a result, an electrostatic latent image is formed on the surface of the image carrier 11.

  In the developing process, the developing unit 14 supplies toner (many toner particles 2) contained in the developer 1 to the electrostatic latent image formed on the surface of the image carrier 11. As a result, the electrostatic latent image is developed as a toner image. The image carrier 11 carries a toner image. The developing unit 14 and the image carrier 11 will be described later.

  In the transfer step, for example, an intermediate transfer method or a direct transfer method can be adopted. In the intermediate transfer method, the primary transfer unit 15 primarily transfers the toner image from the image carrier 11 to the transfer belt 17. Subsequently, the secondary transfer unit 18 secondarily transfers the toner image from the transfer belt 17 to the recording medium P. In the direct transfer method, the primary transfer unit 15 transfers the toner image from the image carrier 11 to the recording medium P conveyed by the transfer belt 17. In the direct transfer method, the image carrier 11 is in contact with the recording medium P when the toner image is transferred to the recording medium P. In the image forming apparatus 100 employing the direct transfer method, the secondary transfer unit 18 is omitted. The toner remaining on the surface of the image carrier 11 after the transfer process is cleaned by the cleaning unit 16 as necessary.

  In the fixing process, the fixing unit 19 fixes the unfixed toner image transferred to the recording medium P by heating and / or pressing. Thereby, an image is formed on the recording medium P.

  The image forming apparatus 100 is not particularly limited as long as it is an electrophotographic image forming apparatus. For example, the image forming apparatus 100 may be a monochrome image forming apparatus or a color image forming apparatus. The image forming apparatus 100 may be a tandem color image forming apparatus in order to form toner images of the respective colors using different color toners. When the image forming apparatus 100 is a monochrome image forming apparatus, the image forming apparatus 100 includes, for example, an image forming unit 10a. The image forming unit 10 a includes an image carrier 11, a charging unit 12, a developing unit 14, a primary transfer unit 15, and a cleaning unit 16. The image carrier 11 is disposed at the center position of the image forming unit 10a. The image carrier 11 is provided to be rotatable in the direction of an arrow (counterclockwise). Around the image carrier 11, a charging unit 12, a developing unit 14, a primary transfer unit 15, and a cleaning unit 16 are sequentially arranged from the upstream side in the rotation direction of the image carrier 11 with the charging unit 12 as a reference. Yes. When the image forming apparatus 100 is a tandem color image forming apparatus, the image forming apparatus 100 includes, for example, image forming units 10a, 10b, 10c, and 10d. The image forming units 10b, 10c, and 10d have the same configuration as the image forming unit 10a.

(Image carrier)
Next, the image carrier 11 will be described in more detail with reference to FIGS. 3 (a) and 3 (b). FIGS. 3A and 3B are partial sectional views of the image carrier 11. As shown in FIG. 3A, the image carrier 11 includes a conductive substrate 111 and a photosensitive layer (corresponding to a photoconductive layer) 112. In the image carrier 11, an electrostatic latent image is formed on the photosensitive layer 112.

  As shown in FIG. 3B, the image carrier 11 may be provided with an undercoat layer (corresponding to a charge injection blocking layer) 113 or a protective layer 114 as necessary. For example, the undercoat layer 113 is provided between the conductive substrate 111 and the photosensitive layer 112. The protective layer 114 is provided as an outermost layer on the photosensitive layer 112, for example.

  The image carrier 11 is an amorphous silicon photoconductor. The amorphous silicon photoconductor has higher wear resistance and durability than the organic photoconductor. However, the amorphous silicon photoreceptor is more likely to cause dielectric breakdown of the photosensitive layer 112 than the organic photoreceptor. Here, the developer 1 of the present embodiment can suppress the occurrence of dielectric breakdown of the photosensitive layer 112 as described above. Therefore, the image forming apparatus 100 using the developer 1 of the present embodiment can suppress the occurrence of dielectric breakdown of the photosensitive layer 112 even when an amorphous silicon photoconductor is provided as the image carrier 11, and black spots in the formed image. Can be suppressed.

  The conductive substrate 111 has a conductive material at least on the surface. For example, the entire conductive substrate 111 may be made of a conductive material. Alternatively, an insulating material (eg, resin or glass) covered with a conductive material may be used as the conductive substrate 111. Examples of the conductive material contained in the conductive substrate 111 include aluminum (Al), zinc (Zn), copper (Cu), iron (Fe), titanium (Ti), nickel (Ni), chromium (Cr), and tantalum. (Ta), tin (Sn), gold (Au), or silver (Ag). A conductive material may be used individually by 1 type, and may be used in combination of 2 or more types (for example, as an alloy). Examples of the conductive material alloy include stainless steel (SUS). Among these conductive materials, aluminum or an aluminum alloy is preferable because of good adhesion to the photosensitive layer 112 and good charge transfer from the photosensitive layer 112 to the conductive substrate 111. The shape of the conductive substrate 111 is, for example, a cylindrical shape.

  The photosensitive layer 112 of the image carrier 11 contains an amorphous (amorphous) silicon-based material. Examples of amorphous silicon-based materials include amorphous silicon containing carbon atoms (a-SiC), amorphous silicon containing carbon atoms and nitrogen atoms (a-SiCN), and amorphous silicon containing nitrogen atoms and oxygen atoms. (A-SiNO), amorphous silicon containing carbon and oxygen atoms (a-SiCO), amorphous silicon containing nitrogen atoms (a-SiN), amorphous silicon (a-Si) or amorphous containing oxygen atoms Silicon (a-SiO) is mentioned. In addition, since it is easy to control the charge mobility in the photosensitive layer 112, it is preferable to further contain at least one atom selected from the group consisting of a hydrogen atom and a halogen atom as a part of the amorphous silicon-based material.

  In order to improve the electrical characteristics of the image carrier 11, the thickness of the photosensitive layer 112 is preferably, for example, 1 μm or more and 100 μm or less.

(Development part)
Next, with reference to FIG. 4, the developing unit 14 that employs the touch-down developing method will be described as an example. The developing unit 14 performs a developing operation. The developing unit 14 can further perform a refresh operation. The developing operation corresponds to the developing step in the image forming method. The refresh operation corresponds to the toner discharging step in the image forming method.

(Development operation)
In the developing operation, the developing unit 14 supplies the toner (a large number of toner particles 2) contained in the developer 1 to the electrostatic latent image formed on the peripheral surface (surface) 11s of the image carrier 11, thereby static electricity. In this operation, the electrostatic latent image is developed as a toner image.

  FIG. 4 shows the developing unit 14 and the image carrier 11 included in the image forming apparatus 100. The developing unit 14 includes a casing 80, a developer conveyance path 81, a developer carrier 82, a toner carrier 83, a developer regulating member 84, and a developer stirring and conveying member 85. The developer carrier 82, the toner carrier 83, and the developer regulating member 84 correspond to a magnetic roller, a developing roller, and a developer regulating blade, respectively. The developer conveyance path 81, the developer carrier 82, the toner carrier 83, the developer regulating member 84, and the developer stirring and conveying member 85 are disposed in the housing 80. The developer 1 is accommodated in the developer conveyance path 81.

  The housing 80 includes a partition wall 801. The developer transport path 81 includes a first transport path 811 and a second transport path 812. The first transport path 811 and the second transport path 812 extend substantially parallel to each other. The partition wall 801 is located between the first transport path 811 and the second transport path 812.

  The developer stirring and conveying member 85 includes a first conveying screw 851 and a second conveying screw 852. A first conveying screw 851 is disposed in the first conveying path 811. A second conveyance screw 852 is disposed in the second conveyance path 812. The first conveying screw 851 and the second conveying screw 852 are disposed substantially in parallel.

  The first conveying screw 851 rotates and conveys the developer 1 in the first conveying path 811 while stirring. Similarly, the second conveying screw 852 rotates and conveys the developer 1 in the second conveying path 812 while stirring. As a result, the developer 1 is conveyed while circulating between the first conveyance path 811 and the second conveyance path 812.

  The developer carrying member 82 faces the developer stirring and conveying member 85 and is rotatably supported by the housing 80. A cylindrical magnet (not shown) is fixed inside the developer carrier 82 so as not to rotate. The magnet has a plurality of magnetic poles. The magnet has, for example, a drawing pole 821, a regulation pole 822 and a main pole 823. The scooping upper electrode 821 faces the developer stirring and conveying member 85. The restriction electrode 822 faces the developer restriction member 84. The main electrode 823 faces the toner carrier 83.

  The developer carrier 82 magnetically pumps (receives) the developer 1 from the developer conveyance path 81 onto the peripheral surface 82 s of the developer carrier 82 by the magnetic force of the scooping pole 821. The developer 1 drawn up is magnetically held as a layer (magnetic brush layer) of the developer 1 on the peripheral surface 82 s of the developer carrier 82. The held developer 1 is conveyed to the developer regulating member 84 as the developer carrier 82 rotates.

  The developer regulating member 84 is provided on the downstream side of the developer stirring and conveying member 85 in the rotation direction of the developer carrier 82. The developer regulating member 84 regulates the layer thickness of the developer 1 that is magnetically attached to the peripheral surface 82 s of the developer carrier 82. The developer regulating member 84 extends along the longitudinal direction of the developer carrier 82. The developer regulating member 84 is a plate-like member made of, for example, a magnetic material. The developer regulating member 84 is supported by a support member 841 fixed to the housing 80. The developer regulating member 84 has a regulating surface 842. The restriction surface 842 corresponds to the tip surface of the developer restriction member 84. A first gap (so-called regulation gap) G1 is provided between the regulation surface 842 and the peripheral surface 82s of the developer carrier 82.

  The developer regulating member 84 is magnetized by the regulating pole 822 of the developer carrier 82. As a result, a magnetic path is formed in the first gap G1 between the regulating surface 842 of the developer regulating member 84 and the regulating pole 822. The layer of the developer 1 adhered on the peripheral surface 82s of the developer carrier 82 by the scooping pole 821 is conveyed into the first gap G1 as the developer carrier 82 rotates. Subsequently, the layer thickness of the developer 1 is regulated in the first gap G1. As a result, a layer of the developer 1 having a predetermined thickness is formed on the peripheral surface 82 s of the developer carrier 82.

  The toner carrier 83 is provided on the downstream side of the developer regulating member 84 in the rotation direction of the developer carrier 82. The toner carrier 83 faces the developer carrier 82 and is rotatably supported by the housing 80. A second gap G <b> 2 is provided between the peripheral surface 83 s of the toner carrier 83 and the peripheral surface 82 s of the developer carrier 82.

The toner carrier 83 rotates while contacting the developer 1 layer formed on the peripheral surface 82 s of the developer carrier 82. Then, predetermined biases are respectively applied to the toner carrier 83 and the developer carrier 82 in the second gap G2. The absolute value V _{83 of the} bias applied to the toner carrier ₈₃ is smaller than the absolute value V _{82 of the} bias applied to the developer carrier ₈₂ . As a result, a predetermined potential difference is generated between the peripheral surface 83 s of the toner carrier 83 and the peripheral surface 82 s of the developer carrier 82. The charging polarity of the toner is the same as the polarity of the bias applied to the toner carrier 83 and the developer carrier 82, for example. Therefore, the toner (many toner particles 2) moves from the developer 1 layer formed on the peripheral surface 82 s of the developer carrier 82 to the peripheral surface 83 s of the toner carrier 83 due to the generated potential difference. Carriers (many carrier particles 5) contained in the developer 1 layer remain on the peripheral surface 82s of the developer carrier 82. Thereby, a layer of toner (many toner particles 2) is formed on the peripheral surface 83s of the toner carrier 83.

  The toner carrier 83 is opposed to the image carrier 11 through an opening formed in the housing 80. A third gap G <b> 3 is provided between the peripheral surface 83 s of the toner carrier 83 and the peripheral surface of the image carrier 11.

The layer of toner (many toner particles 2) formed on the peripheral surface 83s of the toner carrier 83 is conveyed toward the peripheral surface 11s of the image carrier 11 as the toner carrier 83 rotates. Then, a predetermined bias is applied to the toner carrier 83 in the third gap G3. The absolute value V _{83 of the} bias applied to the toner carrier ₈₃ is larger than the absolute value V _11E of the surface potential of the exposure area of the image carrier 11. The absolute value V _{83 of the} bias applied to the toner carrier ₈₃ is smaller than the absolute value V _11UE of the surface potential of the non-exposed area of the image carrier 11. As a result, a predetermined potential difference is generated between the peripheral surface 11 s of the image carrier 11 and the peripheral surface 83 s of the toner carrier 83. The charging polarity of the toner is, for example, the same as the bias applied to the toner carrier 83 and the charging polarity of the image carrier 11. Therefore, due to the generated potential difference, the toner moves from the layer of toner (many toner particles 2) formed on the peripheral surface 83s of the toner carrier 83 to the exposure area of the peripheral surface 11s of the image carrier 11. Thereby, the electrostatic latent image (corresponding to the exposure area) formed on the peripheral surface 11s of the image carrier 11 is developed as a toner image.

(Refresh operation)
The developing unit 14 can further perform a refresh operation in addition to the developing operation. The refresh operation is an operation in which the developing unit 14 discharges toner to the image carrier 11 when the developing unit 14 is not performing development (for example, during non-image formation). The refresh operation is executed, for example, when the printing rate on the recording medium P is below a threshold value. The refresh operation is executed, for example, between sheets of the recording medium P or between print jobs. Between the sheets of the recording medium P, when an image is continuously formed on a plurality of recording media P, after the development operation for forming an image on one recording medium P is finished, the next one sheet This corresponds to the time until the development operation for forming an image on the recording medium P is started. The interval between the print jobs corresponds to a period from the end of a series of print jobs for continuously forming images on a plurality of recording media P to the start of the next series of print jobs.

  In the refresh operation, for example, an electrostatic latent image corresponding to a solid image is formed on the image carrier 11. That is, the entire peripheral surface 11s of the image carrier 11 is set as the exposure area. Then, the developing unit 14 supplies the toner (a large number of toner particles 2) contained in the developer 1 to the electrostatic latent image corresponding to the solid image formed on the peripheral surface (surface) 11s of the image carrier 11. . The operation in which the developing unit 14 supplies the toner to the electrostatic latent image formed on the peripheral surface 11s of the image carrier 11 is the same as the developing operation described above.

  The refresh operation has the following advantages. When images with a low printing rate are continuously formed, the amount of toner supplied from the toner carrier 83 to the image carrier 11 decreases. Therefore, the toner tends to stay in the developing unit 14 for a long time. As a result, the toner in the developing unit 14 may be deteriorated, causing a decrease in image density of the formed image and occurrence of fogging. By performing the refresh operation, the toner can be prevented from staying in the developing unit 14 for a long time. As a result, it is possible to suppress the decrease in the image density of the formed image and the occurrence of fog.

  However, the image forming apparatus 100 including the developing unit 14 that performs the refresh operation easily causes dielectric breakdown of the photosensitive layer 112 of the image carrier 11. This is because a large amount of toner is discharged onto the image carrier 11 during the refresh operation, and the toner tends to stay in a region where the image carrier 11 and the tip of the cleaning unit 16 are in contact with each other. However, as described above, the developer 1 of this embodiment can suppress the occurrence of dielectric breakdown of the photosensitive layer 112 and can suppress the occurrence of black spots in the formed image. Therefore, by using the developer 1 of the present embodiment, it is possible to suppress the occurrence of black spots in the formed image even when the image forming apparatus 100 includes the developing unit 14 that performs the refresh operation.

  As described above, the developing unit 14 adopting the touch-down developing method has been described as an example with reference to FIG. However, the developing method of the developing unit 14 is not particularly limited, and a two-component developing method or other developing methods may be adopted. The developing unit 14 that employs the two-component developing method has the same configuration as the developing unit 14 that employs the touch-down developing method described above, except that the toner carrier 83 is not provided. In the two-component development method, a predetermined bias is applied to the developer carrier 82. As a result, a potential difference is generated between the peripheral surface 11 s of the image carrier 11 and the peripheral surface 82 s of the developer carrier 82. Due to the generated potential difference, the toner (many toner particles 2) moves from the developer 1 layer formed on the peripheral surface 82 s of the developer carrier 82 to the peripheral surface 11 s of the image carrier 11. The carrier (many carrier particles 5) remains on the peripheral surface 82s of the developer carrier 82. Thereby, the electrostatic latent image formed on the peripheral surface 11s of the image carrier 11 is developed as a toner image.

  Examples of the present invention will be described. However, the present invention is not limited to the following examples.

<1. Production of resin particles>
As resin particles for forming toner particles, resin particles A to M were produced by the following method.

(Manufacture of resin particle RA)
A 1000 mL four-necked flask equipped with a stirrer, a condenser tube, a thermometer, and a nitrogen inlet tube was prepared. In a flask, 100 g of butyl methacrylate (BMA), 20 g of styrene, 70 g of divinylbenzene (DVB) as a cross-linking agent, 6 g of sodium dodecylbenzenesulfonate (DBS) as an emulsifier, and benzoylpar as a polymerization initiator 15 g of oxide (BPO) and 600 g of ion-exchanged water were added while stirring. While introducing nitrogen gas into the flask, the contents of the flask were reacted (copolymerized) with stirring at 90 ° C. for 3 hours. As a result, an emulsion of the reaction product (resin particles RA) was obtained. The emulsion of resin particles RA was cooled, washed and dehydrated. As a result, the copolymer particles (resin particles RA) were separated from the emulsion. The number average primary particle diameter of the resin particles RA was 90 nm.

(Production of resin particles RB to RM)
Each of the resin particles RB to RM was manufactured by the same method as that for manufacturing the resin particles RA except that the following points were changed. The addition amount of sodium dodecylbenzenesulfonate (DBS) was changed from 6 g in the production of the resin particle RA to the addition amount shown in Table 1. The addition amount of divinylbenzene (DVB) was changed from 70 g in the production of resin particles RA to the addition amount shown in Table 1. By changing the reaction time of the contents of the flask from 3 hours in the production of the resin particles RA, the number average primary particle diameter of the resin particles is changed from 90 nm of the resin particles RA to the number average primary shown in Table 1. Changed to particle size. In addition, the number average primary particle size of the resin particles increases as the reaction time of the contents of the flask increases.

(Measurement of number average primary particle size)
The number average primary particle diameter of each of the resin particles RA to RM was measured by the following method. Using a field emission scanning electron microscope (FE-SEM, “JSM-3000” manufactured by JEOL Ltd.), the measurement sample (resin particles) was observed at a magnification of 100,000 times. Ten resin particles were randomly selected from the resin particles observed in the field of view of the microscope. The primary particle diameters of the 10 selected resin particles (the diameter of a circle having the same area as the projected area of the resin particles, that is, the equivalent circle diameter) were measured. The sum of the primary particle diameters of 10 resin particles was divided by the number of measured resin particles (10). Thereby, the number average primary particle diameter of the resin particles was calculated.

(Measurement of cohesion degree Y ₁₆₀ )
The aggregation degree Y ₁₆₀ of each of the resin particles RA to RM was measured by the following method. The measurement environment of the degree of aggregation Y ₁₆₀ was a temperature of 23 ° C. and a humidity of 50% RH. As a jig for measuring the agglomeration degree Y ₁₆₀ , a table on which a cylindrical hole (diameter 10 mm, depth 10 mm, material SUS304) is formed, an indenter (diameter 10 mm, material SUS304), and a heater are provided. A jig was used. Note that SUS304 is austenitic stainless steel (iron (Fe) -chromium (Cr) -nickel (Ni) alloy, nickel content 8%, chromium content 18%)).

10 mg of a measurement sample (any of resin particles RA to RM) was put into a cylindrical hole of the jig. While the charged 10 mg measurement sample was heated to 160 ° C., a pressure of 0.1 kgf / mm ² (100 N) was applied to the measurement sample for 5 minutes using an indenter. After applying the pressure, the entire amount of the measurement sample was recovered. The mass of the collected measurement sample (the mass of the measurement sample before separation using a sieve) M _160B was measured.

Thereafter, the collected measurement sample was set on a sieve having a mesh opening of 75 μm (a sieve having 200 mesh, a wire diameter of 50 μm and a plain weave square sieve defined by JIS Z8801-1). The measurement sample was separated from the bottom by suction using a suction machine (“V-3SDR” manufactured by Amano Co., Ltd.). The mass M _160A of the measurement sample remaining on the sieve after separation using a sieve was measured.

Based on the following equation (1), the mass of the measurement sample before separation using the sieve (M _160B ) and the mass of the measurement sample remaining on the sieve after separation using the sieve (M _160A ) The aggregation degree Y ₁₆₀ of the measurement sample at 0 ° C. was calculated.
Y ₁₆₀ (mass%) = 100 × M _160A / M _160B (1)

(Measurement of conductivity)
The conductivity of each dispersion of resin particles RA to RM was measured by the following method. In a beaker, 100 mL of distilled water and 0.1 g of a measurement sample (any of resin particles RA to RM) were placed. The contents of the beaker were subjected to ultrasonic cleaning ("US-18KS" manufactured by SND Co., Ltd.), tank capacity: 18L, high frequency output: 360W, oscillation method: self-excited oscillation by BLT (bolt tightened Langevin type vibrator), oscillation frequency : 38 kHz) for 2 minutes to obtain a dispersion. The conductivity of the dispersion was measured using an electric conductivity meter ("Portable type electric conductivity meter ES-71" manufactured by Horiba, Ltd.).

Table 1 shows the measured number average primary particle diameter, aggregation degree Y ₁₆₀ and conductivity of the resin particles RA to RM. In Table 1, BMA, DBS, BPO, DVB and _Y160 are butyl methacrylate, sodium dodecylbenzenesulfonate (emulsifier), benzoyl peroxide (polymerization initiator), divinylbenzene (crosslinking agent) and 160 ° C., respectively. The degree of aggregation of resin particles is shown. In Table 1, the measurement target of the number average primary particle diameter is resin particles. In Table 1, the measurement target of the conductivity is a dispersion in which 0.1 g of resin particles are dispersed in 100 mL of distilled water.

<2. Production of Developer A-1>
(Manufacture of toner mother particles)
First, toner base particles for manufacturing toner particles were manufactured. The following binder resin, colorant, charge control agent and release agent were used as raw materials for toner base particles.
Binder resin: Polyester resin (acid value 5.6, melting point 105 ° C.)
Colorant: Copper phthalocyanine pigment (CI Pigment Blue 15: 3)
Charge control agent: quaternary ammonium salt ("BONTRON (registered trademark) P-51" manufactured by Orient Chemical Co., Ltd.)
Release agent: ester wax (“Nissan Electol (registered trademark) WEP-3” manufactured by NOF Corporation, melting temperature 73 ° C.)

100 parts by mass of binder resin, 5 parts by mass of release agent, 4 parts by mass of colorant, and 1 part by mass of charge control agent using FM mixer ("FM-10B" manufactured by Nippon Coke Industries, Ltd.) Stir to obtain a mixture. The mixture was kneaded while melting using a twin screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.). The obtained melt-kneaded material was pulverized with a pulverizer (“Turbo Mill RS Model” manufactured by Freund Turbo Co., Ltd.). The obtained pulverized product was classified using a classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.). As a result, toner mother particles were obtained. The obtained toner base particles had a volume median diameter D ₅₀ of 6.8 μm.

(Manufacture of toner)
100 parts by mass of toner base particles and 1 part by mass of hydrophobic silica particles (“AEROSIL (registered trademark) RA-200H” manufactured by Nippon Aerosil Co., Ltd.) are mixed with an FM mixer (“FM-10B manufactured by Nippon Coke Industries, Ltd.”). )) For 5 minutes at 3500 rpm. Subsequently, 1 part by mass of resin particles RA as external additive particles was added to the mixture, and further 5 at a rotational speed of 3500 rpm using an FM mixer (“FM-10B” manufactured by Nippon Coke Industries, Ltd.). Mixed for minutes. As a result, a toner for developer A-1 was obtained.

(Manufacture of carrier C-A)
As the carrier core, a non-coated ferrite core (“EF-35B” manufactured by Powder Tech Co., Ltd., number average primary particle diameter: 35 μm) was used. Next, a carrier coat layer forming solution A was prepared. Specifically, a polyamideimide resin (copolymer of trimellitic anhydride and 4,4′-diaminodiphenylmethane) was diluted with water to prepare a resin solution. A tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA, content of perfluorooctanoic acid: 3 ppm) and polyoxyethylene alkyl ether as a nonionic surfactant were added to and dispersed in the resin solution. As a result, a carrier coat layer forming liquid A was obtained. The solid content concentration of the carrier coat layer forming liquid A was 10% by mass. The mass ratio of the polyamideimide resin and the PFA in the carrier coat layer forming liquid A was 2/8.

  Using a fluidized bed coating apparatus ("Spiraflow (registered trademark) SFC-5" manufactured by Freund Sangyo Co., Ltd.), 50 parts by mass of the carrier coat layer-forming liquid A is fed into the carrier core 1000 while sending hot air at 100 ° C. It sprayed on the mass part. As a result, the carrier core was coated with an uncured organic layer (fluidized bed). The carrier core coated with the uncured organic layer (fluidized bed) was heated at 220 ° C. for 1 hour using a dryer. Thereby, the fluidized bed was hardened. As a result, a carrier CA having a carrier core and a carrier coat layer (a resin layer containing a fluorine-containing resin) covering the carrier core was obtained.

(Mixing of toner and carrier)
9 parts by mass of toner for developer A-1 and 100 parts by mass of carrier CA are mixed with a powder mixer (“Rocking Mixer (registered trademark)” manufactured by Aichi Electric Co., Ltd.), mixing method: container rotation For 30 minutes. As a result, Developer A-1 was obtained.

<3. Production of Developers A-2 to A-7 and B-1 to B-6>
Developers A-2 to A-7 and B-1 to B-6 were produced in the same manner as in the production of Developer A-1, except that the following points were changed. The external additive particles used in the production of the toner are changed from the resin particles RA in the production of the developer A-1 to the types of external additive particles (resin particles RB to RM shown in Table 2). ).

<4. Production of Developer B-7>
Developer B-7 was produced in the same manner as in the production of Developer A-1, except that the following points were changed. The external additive particles used in the production of the toner were changed from the resin particles RA in the production of the developer A-1 to colloidal silica particles having a number average primary particle diameter of 100 nm.

<5. Production of Developer B-8>
Developer B-8 was produced in the same manner as in the production of Developer A-1, except that the following points were changed. The carrier used for mixing the toner and the carrier was changed from the carrier CA in the production of the developer A-1 to the carrier CB. Carrier CB was produced as follows.

(Manufacture of carrier CB)
As the carrier core, a non-coated ferrite core (“EF-35B” manufactured by Powder Tech Co., Ltd., number average primary particle diameter: 35 μm) was used. Next, a carrier coat layer forming solution B was prepared. Specifically, 300 parts by mass of a silicone resin solution (“SR2440” manufactured by Toray Dow Corning Co., Ltd.) and a silane coupling agent (“KBM-403” manufactured by Shin-Etsu Chemical Co., Ltd.), component: 3-glycidoxypropyltrimethoxysilane 3 parts by mass and 300 parts by mass of toluene were mixed and dispersed using a homomixer for 20 minutes. As a result, a carrier coat layer forming liquid B was obtained. The solid content concentration of the carrier coat layer forming liquid B was 50% by mass. The carrier core 1000 was fed with 80 parts by mass of the carrier coat layer forming liquid B using a fluidized bed coating apparatus ("Spiraflow (registered trademark) SFC-5" manufactured by Freund Sangyo Co., Ltd.). It sprayed on the mass part. As a result, the carrier core was coated with an uncured organic layer (fluidized bed). The carrier core coated with the uncured organic layer (fluidized bed) was heated at 250 ° C. for 1 hour using a dryer. Thereby, the fluidized bed was hardened. As a result, carrier CB having a carrier core and a carrier coat layer (a resin layer containing a silicone resin) covering the carrier core was obtained.

<6. Evaluation method>
Using developers A-1 to A-7 and B-1 to B-8 and an evaluation machine, images with different printing rates were formed on paper, and image evaluation was performed. As an evaluation machine, a color compound machine (“TASKalfa 7551ci” manufactured by Kyocera Document Solutions Co., Ltd., image carrier: amorphous silicon photosensitive member, development method: nonmagnetic two-component dry touchdown development method) was used. The developing unit of this evaluator performs a refresh operation (forced toner discharge operation) periodically during non-image formation when an image with a printing rate of 1% is formed. Color / monochrome paper (“C ² ” manufactured by Fuji Xerox Co., Ltd.) was used as the paper. The two-component developer was put into a cyan developing device. In addition, replenishment toner was put into a cyan toner container. The environment in which the image was formed was a temperature of 23 ° C. and a relative humidity of 50% RH.

(Initial image evaluation)
An image N was formed on one sheet using a developer and an evaluation machine. The image N included an image portion with a printing rate of 5%, a blank image portion, and a solid image portion. The image density (initial image density) of the solid image portion of the formed image N was measured. Further, the fog density (initial fog density) of the blank image portion of the formed image N was measured. Table 2 shows the measured initial image density (ID) and initial fog density (FD).

(Image evaluation after printing 100,000 sheets of images with a printing rate of 5%)
An image N was formed on 100,000 sheets of paper using a developer and an evaluation machine. The image N included an image portion with a printing rate of 5%, a blank image portion, and a solid image portion. The image density of the solid image portion of the image N formed on the 100,000th sheet was measured. The fog density of the blank image portion of the image N formed on the 100,000th sheet was measured. Further, the presence or absence of black spots was confirmed in the blank image portion of the image N formed on the 100,000th sheet. Table 2 shows the measured image density (ID), fog density (FD), and evaluation of the presence or absence of black spots.

(Evaluation of images after printing 20,000 images with a printing rate of 1%)
An image L was formed on 20,000 sheets using a developer and an evaluation machine. The image L included an image portion with a printing rate of 1%, a blank image portion, and a solid image portion. The image density of the solid image portion of the image L formed on the 20,000th sheet was measured. The fog density of the blank image portion of the image L formed on the 20,000th sheet was measured. In addition, the presence or absence of black spots was confirmed in the blank image portion of the image L formed on the 20,000th sheet. Subsequently, the surface of the image carrier after printing 20,000 sheets was observed with the naked eye, and the presence or absence of external additive particles on the surface of the image carrier (presence of drum adhesion) was confirmed. When an external additive adheres to the surface of the image carrier, an image defect such as a white spot tends to be caused in the formed image. Table 3 shows the measured image density (ID), fog density (FD), evaluation of presence / absence of black spots, and presence / absence of drum adhesion.

(Image evaluation after printing 10,000 sheets of images with a printing rate of 50%)
An image H was formed on 10,000 sheets of paper using a developer and an evaluation machine. The image H includes an image portion with a printing rate of 50%, a blank image portion, and a solid image portion. The image density of the solid image portion of the image H formed on the 10,000th sheet was measured. The fog density of the blank image portion of the image H formed on the 10,000th sheet was measured. In addition, the presence or absence of a black dot was confirmed in the blank image portion of the image H formed on the 10,000th sheet. Table 4 shows the measured image density (ID), fog density (FD), and the presence or absence of black spots.

(Measurement of image density)
The image density of the solid image portion was measured using a reflection densitometer (“RD914” manufactured by X-rite). 1. A developer on which an image having an image density of 200 or more was formed was regarded as acceptable. 1. A developer having an image density of less than 200 was rejected.

(Measurement of fog density)
The image density of the blank paper image portion was measured using a reflection densitometer (“RD914” manufactured by X-rite). A value obtained by subtracting the image density of the base paper from the image density of the blank paper portion was defined as the fog density. A developer on which an image having a fog density of 0.008 or less was formed was regarded as acceptable. A developer on which an image having a fog density exceeding 0.008 was formed was rejected.

(Check for black spots)
The formed image was checked for the presence of black spots with the naked eye. From the confirmation results, the presence or absence of black spots was evaluated according to the following evaluation criteria. A developer having a black or black evaluation of A or B was considered acceptable. Developers with a black dot evaluation of C were rejected.
Evaluation A: A black spot is not confirmed.
Evaluation B: One or two black spots are confirmed.
Evaluation C: Three or more black spots are confirmed.

Developers A-1 to A-7 contained a toner containing a plurality of toner particles and a carrier containing a plurality of carrier particles. The carrier particles had a carrier core and a carrier coat layer covering the carrier core. The carrier coat layer contained a fluorine-containing resin. The toner particles have toner base particles and a plurality of resin particles provided on the surface of the toner base particles. The number average primary particle diameter of the resin particles was 70 nm or more and 200 nm or less. The conductivity of a dispersion obtained by dispersing 0.1 g of the resin particles in 100 mL of distilled water was 2.5 μS / m or more and 6.0 μS / m or less. The aggregation degree Y ₁₆₀ of the resin particles was 15% by mass or more and 40% by mass or less. Therefore, as shown in Tables 2 to 4, with Developers A-1 to A-7, an initial image, an image with a printing rate of 5%, an image after printing 100,000 sheets, and an image with a printing rate of 1% are 20,000. Both of the image after printing a sheet and the image after printing at a printing rate of 50% were excellent in image density and the occurrence of fog and black spots was suppressed. In Developers A-1 to A-7, the adhesion of external additive particles to the image carrier was suppressed.

In developer B-1, the aggregation degree Y ₁₆₀ of the resin particles exceeded 40% by mass. Therefore, as shown in Table 3, in Developer B-1, external additive particles (resin particles) adhered to the image carrier.

In Developer B-2, the aggregation degree Y ₁₆₀ of the resin particles was less than 15% by mass. Therefore, as shown in Tables 3 and 4, with developer B-2, black dots appear on the image after printing 20,000 sheets of an image with a printing ratio of 1% and the image after printing 10,000 sheets of an image with a printing ratio of 50%. Occurred.

  In developer B-3, the conductivity of the dispersion of resin particles was less than 2.5 μS / m. Therefore, as shown in Tables 3 and 4, with developer B-3, black dots appear on the image after printing 20,000 sheets of an image with a printing ratio of 1% and the image after printing 10,000 sheets of an image with a printing ratio of 50%. Occurred.

  In Developer B-4, the conductivity of the resin particle dispersion exceeded 6.0 μS / m. Therefore, as shown in Table 4, with Developer B-4, fogging occurred in an image after printing 10,000 sheets of an image with a printing rate of 50%.

  In Developer B-5, the number average primary particle size of the resin particles was less than 70 nm. Therefore, as shown in Table 3, with Developer B-5, the image density was low in the image after printing 20,000 sheets of an image with a printing rate of 1%.

  In Developer B-6, the number average primary particle size of the resin particles exceeded 200 nm. Therefore, as shown in Tables 3 and 4, with developer B-6, black dots appear on the image after printing 20,000 sheets of an image with a printing ratio of 1% and the image after printing 10,000 sheets of an image with a printing ratio of 50%. Occurred.

  In Developer B-7, silica particles were provided on the surfaces of the toner base particles, and no resin particles were provided. Therefore, as shown in Tables 3 and 4, with Developer B-7, a black dot appears on the image after printing 20,000 sheets of an image with a printing ratio of 1% and the image after printing 10,000 sheets of an image with a printing ratio of 50%. There has occurred. Further, as shown in Table 4, with Developer B-7, fogging occurred in the image after printing 10,000 sheets of an image with a printing rate of 50%.

  Developer B-8 contained carrier CB. However, the carrier coat layer of carrier CB did not contain a fluorine-containing resin. Therefore, as shown in Table 3, with developer B-8, the image density was low in the image after printing 20,000 sheets of an image with a printing rate of 1%. This is presumably because the toner was overcharged by carrier particles including a carrier coat layer of silicone resin.

  The developer according to the present invention can be used for forming an image by an image forming apparatus such as a printer or a multifunction peripheral. The image forming apparatus and the image forming method according to the present invention can be used to form an image.

DESCRIPTION OF SYMBOLS 1 Developer 2 Toner particle 3 Toner base particle 4 Resin particle 5 Carrier particle 6 Carrier core 7 Carrier coat layer 11 Image carrier 14 Developing part 100 Image forming apparatus

Claims (9)

A developer comprising toner and a carrier,
The carrier includes a plurality of carrier particles,
The carrier particles have a carrier core and a carrier coat layer that covers the carrier core,
The carrier coat layer includes a fluorine-containing resin,
The toner includes a plurality of toner particles,
The toner particles include toner base particles and a plurality of resin particles provided on the surface of the toner base particles.
The number average primary particle diameter of the resin particles is 70 nm or more and 200 nm or less,
The conductivity of a dispersion obtained by dispersing 0.1 g of the resin particles in 100 mL of distilled water is 2.5 μS / m or more and 6.0 μS / m or less,
Cohesion Y ₁₆₀ of the resin particles represented by the following formula (1) is more than 15 wt% 40 wt% or less, the developer.
Y ₁₆₀ = 100 × M _160A / M _160B (1)
(In the formula (1),
M _160B represents the mass of the resin particles to which a pressure of 0.1 kgf / mm ² is applied for 5 minutes at a temperature of 160 ° C.
M _160A separates the resin particles applied with a pressure of 0.1 kgf / mm ² at a temperature of 160 ° C. for 5 minutes using a sieve having an opening of 75 μm, and the resin particles remaining on the sieve after the separation are separated. Represents mass. )   The developer according to claim 1, wherein the resin particles include a copolymer of acrylic acid or an acrylic acid derivative, styrene or a styrene derivative, and a crosslinking agent.   The developer according to claim 2, wherein the content of the crosslinking agent is 35 parts by mass or more and 85 parts by mass or less with respect to 100 parts by mass of acrylic acid or an acrylic acid derivative.   The developer according to claim 1, wherein the fluorine-containing resin is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether.   The developer according to claim 1, wherein the carrier coat layer further includes a polyamideimide resin. An image carrier for carrying a toner image;
The toner contained in the developer according to claim 1 is supplied to an electrostatic latent image formed on a surface of the image carrier, and the electrostatic latent image is converted into the toner image. And developing part for developing as
The image forming apparatus, wherein the image carrier is an amorphous silicon photoconductor.   The image forming apparatus according to claim 6, wherein the developing unit discharges the toner to the image carrier when the developing unit is not performing the development. A developing unit supplies the toner contained in the developer according to any one of claims 1 to 5 to an electrostatic latent image formed on a surface of an image carrier, and the electrostatic latent image is A development step of developing as a toner image,
The image forming method, wherein the image carrier is an amorphous silicon photoconductor.   The image forming method according to claim 8, further comprising a toner discharging step in which the developing unit discharges the toner to the image carrier when the developing unit is not performing the development.

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